Aortic valvular prostheses exhibit greatest hemodynamic limitation, viz., inherent obstruction to flow or so-called prosthetic stenosis, when the smallest sizes are employed. Complex annular reconstructive procedures have been devised to make possible the insertion of larger size prostheses in patients with small aortic roots. We correlated long-term clinical data with serial hemodynamics in 52 patients who received small diameter (17 mm or 19 mm) aortic valvular prostheses without annulus enlargement. No predictors for significant prosthetic stenosis were found for 17 mm Bjork-Shiley valves. Patients with 17 mm Bjork-Shiley valves tended to have greater transprosthetic gradients at rest but effective orifice areas were similar to those found in patients with 19 mm prostheses. Greater transprosthetic gradients did occur in those patients who received 19 mm Bjork-Shiley valves and had greater resting blood flows. Progressive prosthetic stenosis was not observed in patients who underwent multiple postoperative catheterizations over intervals of 2-12 years. It was concluded that acceptable palliation was provided by aortic valve replacement with small diameter prostheses over long periods and that resting hemodynamic studies had limited predictive value for long-term prognosis.